JPS6252866B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic copying machine, and more particularly to an improvement in a charging device.

In electronic copying machines, it is well known that a photoreceptor is charged with a charging device before a document image is exposed to light. Conventionally, the above-mentioned charging device uses corona charging by corona discharge, or contact charging means in which a conductive brush or charging roller is pressed against the photoreceptor to charge the photoreceptor. The above corona charging has the advantage of a simple structure and stable performance, but from 5KV to
Since a high-voltage power supply of 10KV is used, there are safety issues and poor economic efficiency.Furthermore, ozone is generated during corona discharge, and this ozone can significantly change the characteristics of the photoreceptor, developer, and other materials. It has the disadvantage of causing deterioration. In addition, contact charging means requires only a small power source of 0.5KV to 1KV, and since there is no corona discharge, no ozone is generated. However, in this case, there is a drawback that it is difficult to obtain continuous and uniform charging, and reliability is low.
In other words, in conventional contact charging methods, the voltage necessary for charging the photoreceptor is applied in a pulsed manner in one step, and the maximum voltage is applied at the point where the photoreceptor starts contacting the conductive brush or charging roller. Put it away. For this reason, the applied voltage changes rapidly at the point of contact with the photoreceptor, the charge on the photoreceptor is not uniform, and the photoreceptor is easily damaged electrically.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to bring a charging belt into contact with a photoconductor at a peripheral speed different from this circumferential speed, and apply a voltage to them from a power supply means to create a potential gradient. The purpose of the present invention is to provide a charging device for an electronic copying machine which is capable of continuously and uniformly charging performance, is highly safe, and is economical.

An electronic copying machine suitable for employing the apparatus of the present invention will be described below with reference to FIG. A document placement table 2 is provided on the top surface of the main body 1, and this
It is designed to reciprocate by a drive motor 3 disposed inside. At approximately the center of the main body 1, zinc oxide is placed on a drum-shaped conductive substrate (generally kept at a predetermined potential, for example, ground potential in this embodiment) that rotates synchronously with the document mounting table 2. A photoreceptor 4 having a resin-dispersed photoconductor is pivotally supported.
A lamp 5,
An exposure system 7 consisting of an optical fiber lens 6 and the like is provided, and is configured to illuminate the document placed on the document table 2 and guide the reflected light to the photoreceptor 4 to form an image of the document. From this image forming position, the developing device 8, the transfer device 9,
A cleaning device 10 and a charging device 11, which will be described later, are provided. The developing device 8 visualizes the latent image of the document formed on the surface of the photoreceptor 4 by the action of the exposure system 7. The transfer device 9 is for transferring the original toner image formed on the photoconductor 4 onto the copy paper P, and the cleaning device 10 is for removing toner remaining on the surface of the photoconductor 4. At the bottom of the main body 1, there is provided a paper feeding device 14 comprising a removable cassette 12 for storing copy paper P and a paper feed roller 13 for feeding the copy paper P. This paper feeding device 14, the transfer device 9, and a tray 15 protruding from the side of the main body 1 opposite to the paper feeding device are communicated by a conveyance path 16 made of rollers and guide plates. Therefore, the conveyance path 16 guides the copy paper P fed from the paper feeder 14 between the transfer device 9 and the photoreceptor 4, transfers the original image onto the copy paper P, and discharges it onto the tray 15. It's summery. A fixing device 17 faces the conveyance path 16 between the transfer device 9 and the tray 15.
will be placed. This fixing device 17 fixes the original image formed on the copy paper P.

Next, the charging device 11 will be explained. In other words, as shown in FIG. 2, a charging belt 22 is wrapped around a first roller 20 and a second roller 21.
, a drive mechanism 23 that runs endlessly on this charging belt 22, and a power supply means 24. The charging belt 22 has conductivity and has a specific resistance of 10 ⁴ to
10 ¹⁰ Ω・cm is selected. The first and second rollers 20 and 21 are each made of a conductive material,
From both ends, a support shaft 20 made of a conductive material is
a and 21a protrude. Each of the support shafts 20a, 21a is pivotally supported by a bearing (not shown) made of an insulating material, and pulleys 25, 25 made of an insulating material constituting the drive mechanism 23 are fitted into one end of the shaft, and a drive belt 26 is attached to the shaft. It will be handed over. Second roller 21
A driven gear 27 is fitted only to the side support shaft 21a,
A drive gear 2 provided in a drive source (not shown)
8 meshes. Therefore, as the drive gear 28 rotates, the first and second rollers 20 and 21 rotate, and the charging belt 22 runs endlessly in the direction of the arrow in the figure (direction along the rotational direction of the photoreceptor 4). It's becoming like that. At the other end of each support shaft 20a, 21a are terminals 29, 3 that constitute the power supply means 24.
The brushes 29a and 30a provided at 0 are in sliding contact. As shown in FIG. 3, the terminal 29 provided with the brush 29a is grounded via the power supply device 31, and the terminal 30 provided with the brush 30a is directly grounded.

FIG. 4 shows a power supply device 31 that applies voltage to the brush 29a. That is, 32 is an iron resonant transformer, 33 is a diode 33a and a capacitor 3.
This is a rectifier circuit having 3b and the like. Therefore, the ferro-resonant transformer 32 transforms the AC voltage applied to the input terminals 34 and 35 and applies it to the output terminal 37 as well as to the rectifier circuit 33, which applies the transformed AC voltage to the output terminal 37. It's becoming like that.

By electrically connecting in this way, a DC voltage and an AC voltage are applied to the first roller 20 via the brush 29a in a superimposed manner as shown in FIG. Moreover, each of these potentials is a DC voltage, and the Peak to Peak value for this DC voltage is approximately
An AC voltage component of 20% or less is superimposed. Specifically, an AC component of 80V is superimposed on a DC component of approximately 500V. According to the experimental results, if the AC voltage exceeds 100V, which is 20% or more, the photoconductor 4 becomes overcharged.
It was shown that a fatigue phenomenon appeared when the voltage was lower than 50V, and that it was not effective in recovering from fatigue due to continuous use. Therefore, the optimum range of the alternating current to be superimposed is about 80V to about 100V.

As shown in FIG. 6, the characteristics of the iron resonant transformer 32 are such that immediately after input, the voltage exceeds a predetermined voltage, and after approximately 500 mS, the voltage is maintained at the predetermined voltage. In other words, the rise of the output takes approximately
Since 500 mS is required, there is a risk that a stable potential may not be applied to a part of the photoreceptor 4, so timing control is performed so that no image is placed on this part.

Eventually, the power supply means 24 applies a predetermined voltage to the conductive charging belt 22 via the first roller 20. Therefore, the charging belt 22
A predetermined voltage is applied to point B of the photoreceptor 4 shown in the figure. Further, since the charging belt 22 has a specific resistance, it is possible to apply a potential gradient toward the point A of the photoreceptor 4. Since the photoreceptor 4 rotates from point A to point B, the potential it receives has a linear upward slope from point A to point B, as shown in FIG. 7, and ultimately the same amount as before. The potential is . In contrast, conventionally, as shown in FIG. 8, a single charger instantaneously starts up and applies a predetermined voltage, resulting in one-step charging.

By placing an original on the original placing table 2 and pressing a copy button (not shown), each device performs the above-described operations, and the copy paper P on which the original copy image has been obtained is ejected onto the tray 15. In the charging device 11, as the photoreceptor 4 rotates, the drive mechanism 23
operates to rotate the first, second, 20, and 21 in the opposite direction to the photoreceptor 4 and at a slightly slower circumferential speed. Therefore, the charging belt 22 runs endlessly and comes into frictional contact with a portion of the peripheral wall of the photoreceptor 4, but since the peripheral speeds are different, uniform contact is possible, and in the unlikely event that a part of the charging belt 22 is defective (toner Even if stains (such as stains caused by At the same time, a predetermined voltage in which direct current and alternating current are superimposed is applied to the first roller 20 from the power supply device 31 . For this reason, the charging belt 22 applies the voltage to the point B of the photoreceptor 4, and also applies a voltage that sequentially forms a potential gradient from the point having a specific resistance to the point A. Since the photoreceptor 4 rotates from point A to point B, the necessary charging is finally obtained at point B without excessive current flowing into it. By superimposing direct current and alternating current, the effect of space charges generated on the photoreceptor 4 can be prevented and sufficient charging can be achieved in a short time. Specific resistance value of charging belt 22
10 ⁴ to 10 ¹⁰ Ω·cm is the optimum value obtained from various experiments.

As described above, according to the present invention, the drive mechanism causes the charging belt in contact with the photoreceptor to run endlessly at a circumferential speed different from that of the photoreceptor, and the power supply means applies voltage to the charging belt to create a potential gradient. It is something that Therefore, this is similar to applying voltage sequentially to the photoconductor, which eliminates damage to the photoconductor, ensures uniform and continuous charging, and improves safety as no ozone is generated due to charging. do. Furthermore, since the circumferential speeds of the charging belt and the photoreceptor are different, even if there is a part of the charging belt that does not come into contact with the photoreceptor, other parts come into contact with it, so that even charging can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of an electronic copying machine showing an embodiment of the present invention, FIG. 2 is a perspective view of a charging device, FIG. 3 is a schematic side view thereof, and FIG. 4 is a power source in a power supply means. The electric circuit diagram of the device, Figure 5 is its waveform diagram, Figure 6 is a diagram showing the characteristics of the iron resonant transformer, Figure 7 is a diagram explaining the power supply state to the photoreceptor, and Figure 8 is a conventional example of the present invention. It is an explanatory diagram of a power supply state. 4...Photoreceptor, 22...Charging belt, 23...Drive mechanism, 24...Power supply means.

Claims (1)

[Claims] 1. In a device that has a photoconductor on a conductive substrate and charges a rotating photoconductor while the conductive substrate is maintained at a predetermined potential, a charging belt having a specific resistance that contacts the photoconductor; , a drive mechanism that runs this charging belt endlessly and drives it at a peripheral speed different from the peripheral speed of the photoreceptor; The apparatus is characterized by comprising a power supplying electric means for applying a voltage to the charging belt to generate an electric field between the photoreceptor and the charging belt, the intensity of which increases toward the downstream side in the direction of movement of the photoreceptor. A charging device for an electronic copying machine.